as well as the vector \((u-e)\)  for every
\(e\in \mathcal {E}\)  [1]}, which
arises automatically as a valid effect. We also assume that the effect
space spans the full \((d+1)\)  dimensions of the vector space; otherwise
the model would contain states which result in identical probabilities
for all effects in the effect space, making them indistinguishable
and hence operationally equivalent. Note that a \(d\) -dimensional state
space comes with a \(\left(d+1\right)\) -dimensional effect space. Extremal
effects are defined by the property that they cannot be written as
a (non-trivial) convex combination of other effects.
